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Cambridge General Certificate of Education Ordinary Level
5070 Chemistry June 2013
Principal Examiner Report for Teachers

CHEMISTRY
Paper 5070/11
Multiple Choice

Question
Number

Key

Question
Number

Key

1
2
3
4
5

A
D
A
A
B

21
22
23
24
25

D
B
B
C
B

6
7
8
9
10

C
D
C
A
B

26
27
28
29
30

B
D
D
D
B

11
12
13
14
15

C
B
C
D
C

31
32
33
34
35

B
A
B
D
C

16
17
18
19
20

D
B
C
C
A

36
37
38
39
40

A
A
A
B
B

General Comments
Candidates found questions 1 and 39 the most straightforward and the remainder of the paper was a good
test of the candidates’ knowledge and ability.
Comments on Specific Questions
Question 8
Magnesium oxide and aluminium oxide are both ionic compounds and therefore conduct electricity when
molten. The temperature range over which both compounds are molten is 2852 to 2880ºC.
Question 15
Zinc is above copper in the reactivity series and therefore zinc is the metal which ionises in the cell shown in
the question.

1

© 2013

Cambridge General Certificate of Education Ordinary Level
5070 Chemistry June 2013
Principal Examiner Report for Teachers
Question 18
In the reaction between iron(II) sulfate and sodium hydroxide, none of the elements gained or lost electrons.
In all the other reactions elements gained or lost electrons.
Question 23
Calcium proved a strong distractor in this question. The metals calcium and strontium are both in Group II of
the Periodic Table and have similar reactions and in their reactions they lose their two outer electrons.
However, strontium ions and calcium atoms do not have the same electronic configuration.
Question 28
Candidates choosing alternative B concentrated their attention solely on the equations showing the
discharge of ions during the electrolysis of aluminium oxide. However one other reaction, namely the
formation of carbon dioxide, takes place at the positive electrode.
Question 34
Only sulfur dioxide in the list of gases was an acidic gas and able to react with limestone.
Question 38
The only structure without a CH3 group in it was more popular with the candidates than the correct answer A.

2

© 2013

Cambridge General Certificate of Education Ordinary Level
5070 Chemistry June 2013
Principal Examiner Report for Teachers

CHEMISTRY
Paper 5070/12
Multiple Choice

Question
Number

Key

Question
Number

Key

1
2
3
4
5

B
B
C
B
A

21
22
23
24
25

C
C
B
A
D

6
7
8
9
10

C
C
C
B
D

26
27
28
29
30

B
B
A
C
B

11
12
13
14
15

B
D
D
A
C

31
32
33
34
35

D
B
B
B
A

16
17
18
19
20

C
D
B
A
B

36
37
38
39
40

D
C
A
B
A

General Comments
Five questions namely 2, 7, 8, 37 and 39 had very high success rates. Conversely, questions 19 and 35
proved difficult and candidates were split between the four alternatives. Over all the paper distinguished well
between the candidates and proved to be a good test of their chemical knowledge.

Comments on Specific Questions
Question 12
Answers to this question were split between alternatives C and D. The key to obtaining the correct answer
(D) was the realisation that chlorine exists as molecules in the gaseous state.

3

© 2013

Cambridge General Certificate of Education Ordinary Level
5070 Chemistry June 2013
Principal Examiner Report for Teachers
Question 19
Sodium hydroxide is an alkali and reacts with the acidic oxide, carbon dioxide, a fact well known by the
majority of the candidates. Many did not realise that the amphoteric oxide, aluminium oxide, also reacts with
sodium hydroxide.
Question 27
Iron and calcium silicate both settle at the bottom of the Blast Furnace in the liquid state due to the high
temperature of the furnace. The iron is not in the solid state as suggested in distractor D.
Question 28
Nitrogen is almost inert and does not react with copper(II) oxide or sodium hydroxide. The only gas passing
unchanged through the apparatus had to be nitrogen. Thus Z was nitrogen and A was the only alternative
with Z identified as nitrogen.
Question 31
Candidates choosing alternative B concentrated their attention solely on the equations showing the
discharge of ions during the electrolysis of aluminium oxide. However one other reaction, namely the
formation of carbon dioxide, takes place at the positive electrode.
Question 34
The most popular distractor was C, filtration. Filtration is a process used to separate insoluble solids from a
liquid. Thus filtration would not remove salt, a soluble compound, from sea water.
Question 35
Alternatives C was almost as popular as the key, A. Candidates opting for C did not take into account that
A, CH3OH, contained oxygen already and C, C3H8, did not.

4

© 2013

Cambridge General Certificate of Education Ordinary Level
5070 Chemistry June 2013
Principal Examiner Report for Teachers

CHEMISTRY
Paper 5070/21
Theory

Key Messages
To be successful in calculations candidates must organise their answers in a clear and coherent way.
Candidates found the short answer questions less challenging than those which required longer answers. To
improve performance on the latter, it is suggested that candidates answer by using bullet points rather than
long paragraphs in order to better organise their thoughts. Candidates often found it difficult to construct
equations involving ions.

General Comments
Candidates appeared to have sufficient time to compete this examination paper. Most candidates followed
the rubric of the question paper and attempted just three questions from Section B.
Good answers to questions used the correct chemical terms but many candidates gave imprecise answers to
questions that needed a longer response.
Candidates often did not organise their answers to quantitative questions which made it difficult to award
marks for errors carried forward. Candidates should be advised to show all the steps in a calculation so that
Examiners can easily credit the working out.

Comments on Specific Questions
Section A
Question A1
(a)

Some candidates were able to identify iron(II) hydroxide but a common error was copper(II) nitrate.

(b)

Many candidates recognised butane as a saturated hydrocarbon but a common error was propene.

(c)

Some candidates identified propene as a molecule containing nine atoms but other candidates
included some of the ionic compounds. In particular copper(II) nitrate was a popular incorrect
choice.

(d)

Some candidates selected calcium carbonate as a substance used to reduce the acidity in lakes.
Common incorrect responses included iron(II) hydroxide and iron(III) hydroxide.

(e)

Some candidates recognised that sulfur dioxide would give an orange to green colour change with
aqueous potassium dichromate(VI).

(f)

Many candidates selected either sodium chloride or sulfuric acid, the correct responses.

5

© 2013

Cambridge General Certificate of Education Ordinary Level
5070 Chemistry June 2013
Principal Examiner Report for Teachers
Question A2
This question was about photosynthesis.
(a)

The percentage of oxygen in dry air was well known.

(b)

Candidates could often recall the overall equation for photosynthesis. Some candidates included
energy and/or ATP in the equation, this was not given credit. References to chlorophyll or sunlight
over the arrow were ignored.

(c)

The conditions needed for photosynthesis were well known. Some candidates could not
distinguish between reactants and the conditions needed and as a result included carbon dioxide
as a condition. The mark scheme allowed water as a condition since all the reactions take place in
an aqueous solution. The most common correct conditions were sunlight and the presence of
chlorophyll. Not many candidates referred to the presence of enzymes.

(d) (i)

Candidates answered this question with much more confidence than in previous sessions, and
there were far fewer references to bond making needing energy. Good answers stated that bond
breaking was endothermic and bond making was exothermic and then in a second sentence
explained that less energy was released than absorbed.

(ii)

Many candidates could draw a correct energy profile diagram but were less certain when it came to
labelling the energy changes. Typically the activation energy was done better than the enthalpy
change. Often the enthalpy change had the arrow in the wrong direction. Candidates found the
endothermic energy profile much more difficult to label than an exothermic energy profile.

Question A3
This question was about the neutralisation of acids by bases.
(a) (i)

(b)

Some candidates could write the balanced equation although a significant proportion gave the
wrong formula for potassium sulfate.

(ii)

3
Many candidates could interpret the graph and deduced that 24 cm of potassium hydroxide
neutralised the acid. A small proportion of candidates gave a volume of around 39 cm3 where the
graph levelled out.

(iii)

This question had credit for error carried forward from both parts (i) and (ii) however many
candidates did not show their working out or it was so confused it was not possible to see if there
was any credit from error carried forward. A significant proportion of candidates confused the
volumes of acid with the volume of alkali. Good answers gave logical working out and obtained the
correct answer of 0.072 mol/dm3.
Candidates found the preparation of zinc nitrate from zinc oxide extremely challenging. Many
candidates used a titration method to make this salt. Other candidates used a precipitation
method. Only a small proportion of the candidates described the correct preparation using an
insoluble base and dilute nitric acid. Typically candidates scored a mark for appreciating that nitric
acid was needed and sometimes for describing how to obtain crystals from aqueous zinc nitrate

Question A4
This question was about the number of sub-atomic particles in different atoms and ions.
(a)

Some candidates were able to deduce that the nucleon number was 40.

(b)

Candidates did not always specify that the charge on an atom depends on the number of protons
and electrons. A significant proportion of candidates explained this in terms of the equal number of
neutrons and protons (or electrons). Many candidates also forgot to mention the charges on
protons and electrons.

(c)

Candidates often recognised C and D as isotopes, however some gave D and G.

(d)

While candidates often recognised that E was negatively charged not all stated it was -2.

6

© 2013

Cambridge General Certificate of Education Ordinary Level
5070 Chemistry June 2013
Principal Examiner Report for Teachers
(e)

Candidates found this question quite demanding and did not always realise that that it was
connected to the sum of the neutrons and the protons.

Question A5
This question was about ammonium dichromate(VI).
(a)

Candidates were able to show that the formula was (NH4)2Cr2O7 but sometimes they did not show
all the required working out. Only a small proportion of candidates worked out the percentage
composition from the formula and showed that it was the same as that given in the stem of the
question.

(b)

Chromium was often recognised by candidates as the element that was responsible for the colour
of ammonium dichromate(VI).

(c)

Many candidates deduced that the compound was an oxidising agent but few candidates could
explain why, in terms of the change of oxidation state of iodine or the loss or gain of electrons.

(d) (i)

Candidates often recognised the presence of an ammonium ion although there was some
confusion with aluminium ions.

(ii)
(e)

2Candidates found this question very challenging and rarely gave the correct formula of Cr2O7 .

A large variety of compounds containing nitrogen were given as answers including, ammonia,
nitrogen dioxide and nitric oxide. Only a small number gave the correct answer of nitrogen. There
was very little evidence of candidates trying to write an equation and deducing that there were two
nitrogen atoms left which must be the last product.

Question A6
This question was about potassium and chlorine.
(a) (i)

Although some candidates could draw the correct ‘dot-and-cross’ diagram many candidates drew
incorrect diagrams with the outer electrons missing from one or more atoms and only the shared
pairs of electrons being drawn. Most candidates attempted to draw diagrams with the atoms in the
correct order of Cl-O-Cl and only a small proportion of candidates drew ionic ‘dot-and-cross’
diagrams.

(ii)

Candidates found this question extremely challenging and rarely described weak intermolecular
forces. Typical misconceptions included weak covalent bonds or weak forces between atoms.

(b)

Candidates often drew just the outer shell electrons even though the question asked for the
electronic configuration. Other candidates gave the correct electronic structures and either forgot
the charges or wrote down the wrong charges.

(c)

Some candidates were able to write the correct equation using the molar ratios given. Other
candidates tried to write equations with HCl and ignored the information in the stem.

Section B
Question B7
This question focused on malachite.
(a)

Candidates found this question difficult and often only mentioned the formation of gas bubbles.
Some candidates added information about testing the gas with limewater which was not required
by the mark scheme. Candidates were not given credit for reference to a gas being given off since
the question specifically asked for an observation. Most candidates did not describe what
happened to the mixture in terms of forming a blue solution.

(b)

Candidates found this equation extremely challenging and many were not able to give the correct
formulae of the products.

7

© 2013

Cambridge General Certificate of Education Ordinary Level
5070 Chemistry June 2013
Principal Examiner Report for Teachers
(c)

Candidates did not always organise their answers and often presented a collection of numbers and
numerical expressions with no explanation about what they were trying to do. Only a very small
number of candidates got the correct answer of 0.24 g.

(d) (i)

Candidates found this equation extremely challenging and many were not able to give the correct
formulae of the products.

(ii)

Candidates often just expanded on the stem in terms of the finite nature of malachite. The most
popular correct answers focused on less waste and reducing use of landfill sites

Question B8
This question focused on the homologous series of carboxylic acids.
(a)

Candidates often appreciated that members of a homologous series had the same chemical
reactions, though candidates rarely referred to the term functional group. Candidates also
appreciated that members of a homologous series have a general formula or have successive
members that varied by CH2.

(b)

Propanoic acid was well known although a few candidates referred to pentanoic acid.

(c)

The general formula for a carboxylic acid was deduced by many candidates, however candidates
had to include either COOH or CO2H in the general formula rather than just a general molecular
formula.

(d)

Many candidates did not make two statements, one for boiling point and one for melting point.
Candidates needed to appreciate that there was a trend in the boiling point whereas the melting
point did not appear to have a trend.

(e)

Candidates rarely got both the name and the structure of the ester correct. Some candidates
reversed the ester quoting butyl ethanoate rather than ethyl butanoate. A typical error was to miss
out one of the oxygen atoms in the ester and end up having a ketone structure.

(f) (i)

Candidates could often define a weak acid in terms of partial dissociation but found writing the
equation more difficult. Candidates often could not deduce the formula of the hexadecanoate ion.

(ii)

Some candidates wrote an equation showing the formation of the salt and this was given credit.
The most common error was to miss out an oxygen atom giving the formula as C15H31CONa.

Question B9
This question focused on the hydration of ethene.
(a) (i)

Candidates often confused rate of reaction and position of equilibrium and as a result gave
answers that referred to a lower rate of reaction because the reaction was exothermic. Other
candidates just referred to the number of collisions or collision frequency rather than focusing on
the speed of particles and the number of successful collisions. The best answers appreciated that
the rate of reaction increased because there were more successful collisions.

(ii)

Candidates expressed the idea that the position of equilibrium moved to the left in a variety of ways
and often described the backward reaction being favoured. The best answers referred to the
reaction being exothermic so the position of equilibrium moves to the left.

(b) (i)

Candidates often did not appreciate that the particles would be less crowded and that as a result
the collision frequency decreases. Candidates often did not include the idea of collision frequency
and just referred to the number of collisions. Other candidates linked the rate of reaction with le
Chatelier’s principle.

(ii)

As in (a)(ii) candidates expressed the idea that the position of equilibrium moved to the left in a
variety of ways. Only the best answers linked this to the reactants having the greater number of
moles.

8

© 2013

Cambridge General Certificate of Education Ordinary Level
5070 Chemistry June 2013
Principal Examiner Report for Teachers
(c)

Some candidates were able to calculate the energy released as 450 kJ.

(d)

Often candidates not only referred to the lowering of the activation energy but described the idea of
an alternative pathway.

Question B10
This question focused on the electrolysis of aqueous silver nitrate.
(a) (i)

Candidates who could recall the formula of a silver ion were likely to be able to write the cathode
3+
2+
reaction. A common misconception was to give the formula of a silver ion as Ag or Ag .

(ii)

Many candidates were able to recognise that silver ions gain electrons. Other candidates referred
to the correct change in oxidation numbers and this was also given credit in the mark scheme.
Some candidates were careless and referred to silver gaining electrons rather than silver ions.

(b)

Typically candidates were able to get two of the marking points by stating that temperature and
concentration do not affect the mass of silver made. Although candidates often recognised that the
other two factors affected the mass of silver they did not give a precise description of the
relationship i.e. that the current used and the duration were both directly proportional to the mass of
silver produced. Other candidates gave answers that did not use the data but considered the
factors in terms of rate of reaction.

(c)

Some candidates appreciated the significance of ions as the charge carrier but a significant
proportion of the candidates used electrons as the charge carrier. Another misconception was that
solid silver nitrate does not contain ions.

(d)

Candidate rarely could write the ionic equation and even if they did often left the state symbols out.
Most candidates wrote full equations. A typical misconception was to have the formula of silver
chloride as AgCl2.

9

© 2013


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